Piezoelectric components such as, for instance, multilayered piezoelectric actuators consist of a plurality of layers of a piezoelectric material with internal electrodes between the piezoelectric layers. Usually, the same piezoelectric material is used in the entire actuator. Piezoelectric actuators furthermore have a multiplicity of internal electrodes which are arranged one above another and are contact-connected with alternate electrical polarity and between which the piezoelectric material can deform depending on the applied voltage at the internal electrodes. In order for the internal electrodes to be contact-connected in a simple manner, usually only internal electrodes respectively assigned to the same electrical polarity are arranged in a so-called inactive region. The internal electrodes assigned to the other electrical polarity do not extend right to the edge of the actuator at this location, but rather are delimited to an area in the interior of the actuator. Therefore, almost no expansion of the piezoelectric material takes place in the inactive region when an electrical voltage is applied, which leads, in the edge zone of the inactive region, to a tensile loading as a result of the expansion in the active region. Consequently, the tensile stresses occurring at the edge of the inactive region also rise depending on the number of piezoelectric layers and the applied electrical voltage.
The reliability of a multilayered piezoelectric actuator is crucially dependent on combating cracks that may occur. During lamination-thermal processes such as sintering at maximum temperatures of 800 to 1500° C., metallization and soldering and also during polarization, elastic stresses arise on account of the above-described different expansion in the active (driven) and inactive (insulating) region, the elastic stresses leading to so-called load-relieving cracks and/or polarization cracks. These can run in the inactive region or else along an electrode layer. Upon transition into the active region, the cracks can bend away in an uncontrolled manner. If a crack bridges at least two electrodes in this case, short circuits can arise, which leads to the failure of the piezoelectric actuator.
German publications DE 102 34 787 C1 and DE 103 07 825 A1 disclose piezo-electric actuators wherein porous structures are provided, which have less strength than the remaining piezoelectric layers. The increased porosity is produced by using an increased proportion of an organic binder in these regions in comparison with the binder content in the remaining piezoelectric layers.